Design of perfectly matched zero-phase error tracking control for multi-axis motion control systems

This paper focuses on the design of perfectly matched zero-phase error tracking control (PMZPETC) for improving both the tracking accuracy and the contouring accuracy of multi-axis motion systems. For motion systems with multiple axes, the existing zero-phase error tracking control (ZPETC) is usually applied for reducing tracking errors and thus achieving the desired tracking accuracy. However, the contouring accuracy is still limited because the unmatched dynamics among motion axes, and thus some advanced contouring controllers are used to further improve contouring accuracy in motion. In this paper, for simplifying the design complexity of multi-axis motion controllers and for improving the contouring accuracy of applying ZPETC in multi-axis motion systems, a perfectly matched ZPETC (PMZPETC) for multi-axis motion systems is designed by considering the mutual dynamics of all motion axes. In the multiple feedforward control loops, applying stable pole-zero cancellation to each axis and compensating phases for the uncancelled zeros of all axes lead to the perfectly matched dynamic responses of all motion axes across the whole frequency range. Thus, the tracking accuracy and the contouring accuracy for multi-axis motion systems are both guaranteed. Moreover, since the present model-based design is sensitive to uncertainties in real applications, the disturbance observer (DOB) is also applied to each axis for the enhancement of axial robustness. Finally, some simulations and experiments on a 3-axis CNC machining center are taken to verify the PMZPETC design, and the results shows that the PMZPETC design significantly improves both the contouring accuracy and the tracking accuracy of multi-axis motion systems.